Hi Virginia,
Please navigate to the list of CDNs in the Azure portal:
Click on your Classic CDN. Next click on Settings -- Migration, then click Validate button:
If no errors then continue on to Prepare for migration step. If you have specific questions please add a comment. Below article details the steps to migrate:
Migrate Azure CDN from Microsoft (classic) to Standard/Premium tier
https://learn.microsoft.com/en-us/azure/cdn/migrate-tier
Please click Accept Answer and upvote if the above was helpful.
Thanks.
-TP